For the purpose of observation of a micro region of an object, electron scanning electron microscopes (SEMs) and transmission electron microscopes (TEMs) are used, for example. These devices are typically configured to evacuate an enclosure thereof in which a sample is to be placed and then to image the sample in the vacuum atmosphere. Some samples such as biological and chemical samples and liquid samples, however, may be damaged with the vacuum or may change in state. Meanwhile there is a great need for observation of such samples with electron microscopes, and so SEM apparatuses and sample holding devices enabling the observation of a sample to be observed at atmospheric pressure have been developed recently.
These devices are designed on the principle of providing a diaphragm or a small aperture between an electron optical system and a sample so as to let an electron beam pass therethrough, thus partitioning the vacuum state and the atmospheric state, and they are common in including a diaphragm between a sample and an electron optical system.
Patent Literature 1, for example, discloses a SEM including an electron optic column disposed so that the electron source side thereof is directed downward and the objective lens side thereof is directed upward, and a diaphragm disposed above the exit aperture of an electron beam at the end of the electron optic column via an O ring so as to transmit an electron beam. In the invention described in this literature, a sample to be observed is directly placed on the diaphragm, a primary electron beam is applied to the sample from the lower surface thereof, and reflected electrons or secondary electrons are detected for SEM observation. A sample is held in a space defined with an annular member disposed around the diaphragm and the diaphragm, and this space is filled with liquid such as water.